Chasing Schottky-Mott: Metal-first non-alloyed contacts to β-Ga₂O₃ for interface quality and minimal surface modification

Metal-first non-alloyed ohmic and Schottky contacts are fabricated on β -Ga 2 O 3 with a range of metal work functions ( ϕ M ). The resulting ohmic contacts are of high quality with a contact resistance ( R c ) as low as 0.069 ± 0.003 Ω mm. Measurements of the barrier heights ( ϕ B ) indicate that metal-first processing, which preserves the as-grown/bare-substrate surface, also partially un-pins the Fermi-level in (010) and ( 2 ¯ 01) oriented Ga 2 O 3 . Depth-resolved XPS (x-ray photoelectron spectroscopy) measurements of the oxidation state throughout the contact metal at the contact- Ga 2 O 3 interface indicate that most non-alloyed contact metals are at least partially oxidized by room temperature redox reactions with the underlying Ga 2 O 3 , with metals with a lower ϕ M also demonstrating the greatest level of oxidation. As oxidation has been previously observed to enhance a metal’s work function, this may imply that to-date observations of indices of surface behavior << 1 on β -Ga 2 O 3 , which have been attributed to severe Fermi-level pinning, may need to be corrected to account for this partial oxidation in addition to other surface modifications during device processing demonstrated in this work.